Continuous lead-in core for an electrode assembly

ABSTRACT

An electrode assembly is provided for an electrolytic cell which comprises a substantially horizontally extending foraminate titanium structure carrying on at least a part of its surface a coating comprising an operative anode material, an array of parallel spaced rods approximately covering the area of said foraminate structure, each rod having a titanium casing which is rigidly and conductively connected along its length to the upper surface of said foraminate structure and is also attached to the titanium casing of at least one rectangular bar which passes transversely over said rods by welds which enclose in fluid-tight manner intercommunicating openings through the juxtaposed areas of the casings of said rod and said bar, the casing of each said rectangular bar having an opening in its upper face, and attached in fluid-tight manner to said upper face to enclose said opening an upstanding wall of titanium sheet, the space within said upstanding wall and the titanium casings of said bar and said rods being substantially filled by a continuous core of aluminum or an aluminum alloy, said core being bonded to the surrounding titanium surfaces by an inter diffusion layer of an alloy formed between the core metal and the surrounding titanium metal.

United States Patent King etal.

[ 1 June 20, 1972 CONTINUOUS LEAD-IN CORE FOR AN ELECTRODE ASSEMBLY [72]Inventors: John I-Iowllston King; Frank Smith, both of Runcorn, England[22] Filed: Aug. 21, I970 [21] Appl.No.: 66,034

[73] Assignee:

[30] Foreign Application Priority Data Sept. 2, 1969 Great Britain.43,329/69 [52] [1.8. CI ..204/284, 204/286, 204/290 F [5 l] Int. Cl.BOlk 3/04, C23b 5/68, C23b 5/74 [58] Field of Search ..204/290 F, 290R, 284, 286, 204/288, 278, 99, 250

[56} References Cited UNITED STATES PATENTS 3,318,792 5/1967 Cotton etal ..204/290 F X 3,409,533 l l/l968 Murayama et al. ....204/250 X3,380,908 4/l968 Ono et al. ....204/290 F 3,507,771 4/1970 Donges et al.....204/290 F 3,562,008 2/l97l Mantinsons 204/290 F 3,297,561 l/l967Harrison et al. ..204/290 F X FOREIGN PATENTS OR APPLICATIONS 1,045,96610/ l 966 Great Britain ..204/290 F Primary Examiner-John H. MackAssistant ExaminerRegan J. Fay Attomey-Cushman, Darby & Cushman ABSTRACTAn electrode assembly is provided for an electrolytic cell whichcomprises a substantially horizontally extending foraminate titaniumstructure carrying on at least a part of its surface a coatingcomprising an operative anode material, an array of parallel spaced rodsapproximately covering the area of said foraminate structure, each rodhaving a titanium casing which is rigidly and conductively connectedalong its length to the upper surface of said foraminate structure andis also at tached to the titanium casing of at least one rectangular barwhich passes transversely over said rods by welds which enclose influid-tight manner intercommunicating openings through the juxtaposedareas of the casings of said rod and said bar, the casing of each saidrectangular bar having an opening in its upper face, and attached influid-tight manner to said upper face to enclose said opening anupstanding wall of titanium sheet, the space within said upstanding walland the titanium casings of said bar and said rods being substantiallyfilled by a continuous core of aluminum or an aluminum alloy, said corebeing bonded to the surrounding titanium surfaces by an inter diffusionlayer of an alloy formed between the core metal and the surroundingtitanium metal.

7 Claims, 5 Drawing Figures PATENTEDJUMO 1972 saw 2 or 3 CONTINUOUSLEAD-IN CORE FOR AN ELECTRODE ASSEMBLY The present invention relates toan anode assembly for an electrolytic cell. More particularly it relatesto an anode assembly that is particularly useful in a mercury-cathodecell for the electrolysis of alkali metal chloride solution.

In recent years it has been proposed to install in cells for themanufacture of chlorine, hypochlorites and chlorates by the electrolysisof alkali metal chloride solutions so-called permanent anodes instead ofthe conventional graphite anodes which wear away at an appreciable ratein use. The permanent anode comprises a supporting structure made of afilm-forming metal, usually titanium, carrying a coating of an operativeanode material, i.e. a material which is capable of transferringelectrons from the electrolyte to the supporting structure of the anodeand which is resistant to electrochemical attack in the cell. Theearliest coatings were platinum group metals and/or their oxides. Morerecently it has been proposed to use a number of other conducting andsemiconducting materials which have the necessary catalytic propertiesand wear resistance to function as anode coatings.

In a mercury-cathode cell where the working anode surface is anapproximately horizontal plane parallel to the flowing mercury cathodeand where chlorine gas is evolved at the anode arrangements must be madefor the gas to escape rapidly upwards as it is formed and there havebeen several proposals for providing the necessary openings for theescape of gas in coated titanium anode structures. For example it hasbeen proposed to make the horizontally extending titanium support whichcarries the active coating from a multi-holed titanium sheet of expandedmetal or to build it up as a spaced parallel array of titanium rods,narrow strips or other longitudinally extending profiles held togetherby transverse ribs and to suspend this structure from a central pillarwhich passes through the cover of the cell and also acts as the currentleadin. Anode assemblies of this type cannot, however, provide goodcurrent distribution over the whole working area of the anode unless thehorizontal member or members that carry the active coating are madeundesirably thick and expensive. The present invention provides an anodeassembly in which the current distribution is considerably improved,which is resistant to mechanical distortion and which also enables alowresistance connection to be made to an electrical bus-bar outside thecell.

According to the present invention we provide an anode assembly for anelectrolytic cell which comprises a substantially horizontally extendingforaminate titanium structure carrying on at least a part of its surfacea coating comprising an operative anode material, an array of parallelspaced rods approximately covering the area of said foraminatestructure, each rod having a titanium casing which is rigidly andconductively connected along its length to the upper surface of saidforaminate structure and is also attached to the titanium casing of atleast one rectangular bar which passes transversely over said rods bywelds which enclose in fluid-tight manner intercomrnunicating openingsthrough the juxtaposed areas of the casings of said rod and said bar,the casing of each said rectangular bar having an opening in its upperface, and attached in fluid-tight manner to said upper face to enclosesaid opening an upstanding wall of titanium sheet, the space within saidupstanding wall and the titanium casings of said bar and said rods beingsubstantially filled by a continuous core of aluminum or an aluminumalloy, said core being bonded to the surrounding titanium surfaces by aninter diffusion layer of an alloy formed between the core metal and thesurrounding titanium metal.

In a preferred embodiment of the invention the opening in the upper faceof the casing of each rectangular bar is a rectangular opening and theupstanding titanium wall is also made rectangular and is attached to theupper face of the bar by a continuous weld around the periphery of thesaid opening so as to provide a large intercomrnunicating area betweenthe core metals of these components.

The substantially horizontally extending foraminate titanium structurewhich carries the coating comprising an operative anode material may bea multi-holed titanium sheet, e.g. a sheet of expanded titanium metal,or a louvred structure such as may be obtained by pressing out louvresfrom a titanium sheet by means of a slitting and forming tool. Thelouvre slats so obtained may suitably be turned at right angles to theoriginal plane of the titanium sheet or they may have each of theiredges rolled round to form approximately hemicylindrical memberscorresponding with the slots from which the metal forming them has beenpressed out. A suitable multiholed titanium sheet may also be formed byisostatic pressing of titanium powder, i.e. compacting the powder byhydraulic pressure applied to a flexible mould containing the powder,which is immersed in the hydraulic fluid. The compact is then sinteredat about l,050 C. Alternatively the foraminate titanium structure may bebuilt up from longitudinally-extending titanium members spaced apartwith their long axes parallel to each other, running transverselybeneath the supporting array of aluminum-cored titanium rods and rigidlyand conductively connected, e.g. by welding, to the titanium casing ofeach of the said rods. The longitudinally-extending titanium memberswhich form the foraminate titanium structure may be for instance flatstrips, rods, hemicylindrical channels which are convex upwards orconvex downwards, or channels of U- shape or inverted U-shape, theclosed end of the U being optionally flattened.

In this specification by titanium" we mean titanium metal alone or analloy based on titanium and having anodic polarization propertiescomparable to those of titanium as known in the art.

The operative anode material may be any material which is active intransferring electrons from an electrolyte to the underlying titaniumstructure of the anode assembly and which is resistant toelectrochemical attack under the conditions ruling in the cell where theanode is to be used. For use in very corro sive media, for instance inchloride electrolytes, the operative anode material may suitably consistof one or more platinum group metals, i.e. platinum, rhodium, iridium,ruthenium, osmium and palladium, and/or oxides thereof or another metalor a compound which will function as an anode and is resistant toelectrochemical dissolution in the cell, for instance rhenium, rheniumtrioxide, magnetite, titanium nitride and the borides, phosphides andsilicides of the platinum group metals. The coating comprising anoperative anode material may also contain oxidic semiconductingcompounds or again it may contain electronically non-conducting oxides,particularly oxides of the film-forming metals such as titanium, as isknown in the art, to anchor the operative anode material more securelyto the supporting titanium structure and to increase its resistance todissolution in the working cell. A preferred coating for anodes that areto be used in mercury-cathode cells electrolyzing alkali metal chloridesolutions consists of at least one oxide of at least one platinum groupmetal, particularly ruthenium dioxide, as the operative electrodematerial. and titanium dioxide.

In British Pat. Specification No. 1,045 ,966 there is described a methodfor the manufacture of aluminum-cored titanium conductors, generally ofrod shape suitable for fitting at one end to a graphite anode block or aplatinum-coated titanium sheet anode. The current distributing structureof the present anode assembly consisting of a continuous core ofaluminum or an aluminum alloy within a titanium casing is suitablymanufactured by substantially the same method, of which the essentialsteps are l) removing any oxide skin from the internal surface of thetitanium casing, (2) substantially filling the casing with molten coremetal, (3) maintaining the filled casing at a temperature between themelting points of the casing and the core metal for a time sufiicient toform a titanium/core metal interdiffusion alloy zone at thetitanium/core metal interface and then (4) allowing the core metal tosolidify by cooling, steps 2, 3 and 4 being carried out in an inertatmosphere, e. g. an argon atmosphere.

The oxide skin may be removed from the titanium casing by pickling in amixture of 20% nitric acid and 4% hydrofluoric acid after degreasing asnecessary. It is also preferred to pickle the core metal in 30% causticsoda solution to remove any protective lubricant and oxide beforemelting. Furthermore, the internal surfaces of the titanium casing,after removal of the oxide skin therefrom, may be coated with a metalchloride/fluoride flux before filling with the core metal to aid alloybonding of the casing with the core metal.

The time of heating the molten core metal in contact with the titaniumcasing should not be unnecessarily prolonged so as to avoid creating somuch interdiffusion as might weaken the resistance of the titaniumcasing to corrosive conditions. When the core metal is commercially purealuminum a suitable time and temperature are 30 minutes at 700 C. Thetime should be reduced at higher temperatures eg to about 5 minutes at800 C. Lower temperatures are possible if a lowermelting aluminum alloyis used as the core metal, for instance an alloy of aluminum with one ormore of silicon, copper and magnesium, and containing a major proportionof aluminum. At 500 C a suitable time of heating to form the alloy bondis about 6 hours.

Suitable methods of manufacturing the aluminum-cored structure whichsupports the working anode surface in an anode assembly according to theinvention will be further discussed in relation to the accompanyingdrawings, wherein FIG. I shows in isometric projection one embodiment ofsuch an assembly and also shows a method of connecting an electricalbus-bar thereto,

FIGS. 2-4 illustrate in part sectionalelevation methods of filling thecore metal into the titanium casing during the manufacture of suchassemblies and FIG. 5 shows in part elevation a suitable method ofinstalling an anode assembly according to the invention in anelectrolytic cell.

In FIG. I, each of two current lead-in members 4 consisting of anupstanding rectangular titanium sheet wall surrounding an aluminum corecarry the current to a primary current distributor member 3 consistingof a hollow rectangular box of titanium sheet enclosing an aluminumcore. The upstanding titanium wall of the current lead-in member 4 iscontinuously welded around the periphery of a rectangular opening in theupper face of the titanium casing of the primary current distributormember 3 so that the spaces enclosed by the wall of member 4 and thecasing of corresponding member 3 are intercommunicating through the saidopening. Each primary current distributor member 3 carries current to aparallelspaced array of secondary current distributor members 2, each inthe form of a rod consisting of an aluminum core within a titanium tubehaving a titanium closure at each end. The juxtaposed areas of thetitanium tube of each member 2 and the titanium casings of members 3have intercommunicating openings and these tubes and casings are weldedtogether in fluid-tight manner around the said openings to formpassage-ways between the spaces enclosed by each tube and the casings ofthe members 3.

Referring again to FIG. 1 of the drawing, 1 is a substantiallyhorizontal extending sheet of expanded titanium metal carrying a coatingcomprising an operative anode material to form a working anode surface.This is supported from above by bonding it to the titanium casings ofeach of the secondary current distributor members 2 along the lengththereof. Because of the good current distribution to the expanded metalsheet 1 and the mechanical strength of the whole structure, the expandedmetal sheet may be of quite light gauge and may be bonded to thetitanium casings of the secondary current distributors 2 directly, forinstance by electrical-resistance welding, or may be connected theretoby electricalresistance welding or argon are spot welding it to a seriesof titanium studs which have been fixed to the said titanium casings bya capacitor discharge stud-welding process, thus avoiding anysignificant heating such as might cause distortion or damage.

The expanded metal sheet 1 may be welded in the abovedescribed manner tothe secondary current distributor members 2 before or after applying thecoating comprising an operative anode material to the sheet. We havefound, however, that when the expanded metal sheet is fixed to thecurrent distributor members before applying the active anode coating,steps must be taken to prevent distortion of the sheet during thesubsequent coating operation if the coating method involves heating theanode assembly to temperatures such as would cause significantdifferential expansion between the aluminum-cored supporting network andthe sheet, as for instance the conventional method of producing coatingscomprising platinum group metals and/or their oxides by applying paintcompositions containing compounds of the platinum group metals and thenheating at a temperature of about 450 C or higher. Such distortion canbe avoided or reduced to an insignificant extent by cutting the expandedmetal sheet into sections and welding one section to each of thesecondary current distributor members 2. Any minor distortions that dothen occur during a subsequent heating step can easily be corrected bysimple pressing, whereas we have found that distortion caused in thisway in a full-area sheet cannot subsequently be corrected. Likewise whenthe foraminate titanium structure is built up from longitudinallyextending members spaced apart parallel to each other, e.g. titaniumstrips, distortion in a subsequent hot-coating step can be avoided bycutting each member into short sections. The most suitable procedure isto weld the uncut members to each of the current distributors 2 and thento make narrow expansion gaps in each member by running a saw throughthem between each pair of neighboring welds before carrying out thehot-coating step.

It will be seen that in the structure described with reference to FIG. 1of the drawings the titanium casings of current leadin members 4,primary current distributor members 3 and secondary current distributormembers 2 form an integral fluid-tight casing with only the upper facesof the lead-in members 4 open and that the spaces enclosed thereby areall intercommunicating one with the next. According to the invention thealuminum core within this integral casing is one continuous core. It isformed by freezing a filling of aluminum from the molten state thereinafter alloy-bonding to the surrounding casing for the appropriate timein the molten state as described hereinbefore.

In manufacturing the assembly, the aforesaid integral titanium casing ofmembers 2, 3 and 4 may all be welded together, and after cleaning,etching and heating to the required temperature may be filled with themolten core metal through the open tops of the current lead-in members 4in an argon atmosphere. Perfect filling of the cross-section of eachmember is not essential so long as continuity is adequately establishedbetween the neighboring members. We have found that adequate filling ofthe intricate array of tubes can be achieved through the open tops ofthe current lead-in members by rocking the assembly from side to sideand end to end as the molten core metal is introduced.

If desired, however, more perfect filling of the remote tubes of currentdistributors 2 may be ensured by placing a loosely fitting aluminum rodin each of these before closing the titanium end caps, then heating thestructure to melt these rods and completing the filling through the topopenings of the current lead-in members 4. FIG. 2 of the accompanyingdrawings illustrates the preferred form of titanium end closure for thetitanium tubes of current distributors 2 when this second method offilling is used. In FIG. 2 shown in longitudinal section on a largerscale an end portion 6 of the titanium tube of one current distributor 2of FIG. 1 with a loosely fitting aluminum rod 7 placed inside. Atitanium end closure 8 has then been inserted and sealed in place bywelding around the end of the tube as indicated at 9, thus avoidingoverheating of the aluminum rod during this welding operation.

When molten aluminum is held in an open-topped titanium casing it has amarked tendency to creep up the titanium walls and can even overflow andrun down the outside of the walls unless these are much higher than thegeneral level of the molten aluminum. There is also considerabledifferential shrinkage of the core from the top when a molten aluminumcore is allowed to freeze in an open-topped titanium casing. If,therefore, the integral titanium casing of members 2, 3 and 4 of FIG. 1is filled with the molten core metal directly through the open tops ofthe current lead-in member 4 the result after the hot alloy-bondingstage and subsequent cooling will be somewhat as shown in FIG. 3. Thisfigure shows in schematic form a vertical section through part of aprimary current distributor 3 with its attached current lead-in member4. It will be seen that in order to remove the creep and shrinkagedefects of the core metal 11 a considerable length of the titanium wallsof the current lead-in member 4 would also have to be cut away. Thiswaste can be avoided by clamping around the open top of the titaniumwalls of the current lead-in member 4 an extension made of a materialwhich is not wetted by the molten core metal, before the core metal isintroduced. A suitable arrangement is shown in FIG. 4, wherein a steelbox 12 has been employed to clamp an aluminum silicate refractory fiberblanket 13 around the open top of the titanium walls 10. The resultafter filling with the core metal, hot alloy-bonding of the core to thetitanium and subsequent cooling is then as shown in FIG. 4. Only thedefect clue to shrinkage in the core remains to be removed, withoutwaste of the titanium retaining walls 10.

An anode assembly according to the invention, for instance theembodiment comprising parts 1-4 of FIG. 1 of the accompanying drawings,is installed in a cell by passing each current lead-in 4 through anopening provided in the cell cover and pulling it up to seat the upperface of the primary current distributor 3 against resilient gasket-meanswhich has been applied around the lead-in 4. This may be done in themanner shown in FIG. 5, wherein parts l-4 refer to the same parts of theanode assembly as in FIG. 1. The assembly is installed in the cell bytapping a threaded spindle 14 into the aluminum core of the lead-in 4,passing the spindle through a conventional bridge-piece l5 resting onthe cell cover 16 and tightening downwards on to the bridge piece a nut17 running on the spindle so as to pull the spindle upwards and compressgasketmeans 18 which has been applied around the lead-in 4 to make afluid-tight joint.

In FIG. 1 of the accompanying drawings there is also shown a method ofattaching a bus-bar outside the cell to the anode assembly. The upperface of each current lead-in 4 is machined to a true plane so that abus-bar 5, suitably of aluminum, can be secured to it (by bolts notshown) to make good electrical contact with the exposed aluminum core ofthe lead-in 4. The aforesaid spindle used to pull the anode assemblyinto place in the cell with the aid of a bridge-piece will then passdown into the aluminum core of the lead-in 4 through the bus-bar 5.

In other embodiments of the invention there may be only one primarycurrent distributor member 3, which will then be placed centrally acrossthe array of secondary current dis tributor members 2. Conversely in alarger assembly there may be more than two primary current distributormembers 3 suitably spaced apart. Furthermore the current lead-in 4,which is shown in the drawing as offset towards one end of thecorresponding current distributor member 3, may be placed centrally overa central opening in the titanium casing of the member 3.

What we claim is:

1. An anode assembly for an electrolytic cell. which comprises asubstantially horizontally extending foraminate titanium structurecarrying on at least a part of its lower surface a coating comprising anoperative anode material. an array of parallel-spaced titanium tubesapproximately covering the area of said foraminate structure, each tubebeing rigidly and conductively connected along its length to the uppersurface of said foraminate structure and is also attached by welds to atleast one titanium casing which passes transversely over said tubes,said casing and said tubes havin intercommunicatin uxtaposed openingsenclosed by sai titanium casing an tubes in fluid-tight manner, saidcasing having an opening in its upper face, and attached in fluid-tightmanner to said upper face of said titanium casing to enclose saidopening an upstanding current lead-in casing of titanium sheet, thecommunicating spaces within said upstanding current lead-in casing andthe titanium casing and said tubes being substantially filled by anintegral continuous core of aluminum or aluminum alloy, said core beingbonded to the surrounding titanium surfaces by an inter diffusion layerof an alloy fored between the core metal and the surrounding titaniummetal.

2. An anode assembly according to claim 1, wherein the opening in theupper face of the casing is a rectangular opening and the upstandingcurrent lead-in casing enclosing said opening is attached to the saidupper face by a continuous weld around the periphery of the said openingto form a rectangular enclosure.

3. An anode assembly according to claim 1, wherein the foraminatetitanium structure is a sheet of expanded titanium metal.

4. An anode assembly according to claim 3, wherein each of the saidtubes is connected to the expanded titanium metal sheet by a series oftitanium studs, each of which is welded to the tube and the sheet.

5. An anode assembly according to claim 1, wherein the foraminatetitanium structure has been built up from longitudinally extendingtitanium members spaced apart with their long axes parallel to eachother.

6. An anode assembly according to claim 1, wherein the anode material isa material selected from the group consisting of a platinum group metaland an oxide of a platinum group metal.

7. An anode assembly according to claim 1, wherein the coating consistsof at least one oxide of at least one platinum group metal and titaniumdioxide.

2. An anode assembly acCording to claim 1, wherein the opening in theupper face of the casing is a rectangular opening and the upstandingcurrent lead-in casing enclosing said opening is attached to the saidupper face by a continuous weld around the periphery of the said openingto form a rectangular enclosure.
 3. An anode assembly according to claim1, wherein the foraminate titanium structure is a sheet of expandedtitanium metal.
 4. An anode assembly according to claim 3, wherein eachof the said tubes is connected to the expanded titanium metal sheet by aseries of titanium studs, each of which is welded to the tube and thesheet.
 5. An anode assembly according to claim 1, wherein the foraminatetitanium structure has been built up from longitudinally extendingtitanium members spaced apart with their long axes parallel to eachother.
 6. An anode assembly according to claim 1, wherein the anodematerial is a material selected from the group consisting of a platinumgroup metal and an oxide of a platinum group metal.
 7. An anode assemblyaccording to claim 1, wherein the coating consists of at least one oxideof at least one platinum group metal and titanium dioxide.